Polyurethane foams, formed by the reaction of a polyisocyanate with a polyhydroxyl-containing compound in the presence of a suitable catalyst, are widely accepted as padding materials for cushions in furniture, automobiles and the like. Polyurethane foams are also used as sponges and for other uses that require liquid absorption properties, such as specialty packaging and personal care and hygiene items. Typically, the foams are made in the form of slabs, which are cut to shape, or they are molded to specific needs.
Molded foams are commonly of the "high resilience" (HR) type, and are characterized by high sag factors and improved hysteresis curves compared to the usual slab foams. HR foams are often crushed to give the foams sufficient "breathability" since HR foams tend to have a high percentage of closed cells.
Foam static fatigue, as measured by compression set data, or the ability of the foam to recover after it is compressed by a certain amount, is a constant concern to the end user of the foam, as it is a measure of durability. Limits of acceptability are typically specified by the foam purchaser.
It would be useful to devise an improved HR polyurethane composition employing one additive which could improve the static fatigue properties. If another property, such as the flammability-resistance characteristics of the resultant HR foam could also be improved, it would be an added bonus. While it is known that phosphorus compounds, such as halogenated phosphate compounds, serve as flame retardants in flexible polyurethane foams, such flame retardants are not used in HR flexible foams because these HR foams typically pass flammability characteristic tests without additives. Thus, one skilled in the art would not be motivated to and would not be expected to add flame retardants to HR polyurethane foams.